Ceop says senders can also find they become victims of bullying or harassment.

Meanwhile, a survey by the Beatbullying charity suggested one in five 11 to 17-year-olds has received a sexually explicit or distressing text or e-mail.

The charity spoke to 2,094 young people for the survey, carried out in 2009.

Some 70% of those who have received an explicit text or e-mail said they knew the sender.

Ceop chief executive Peter Davies said: "We know that young people are increasingly using technology not only to stay in touch, but to explore their sexuality and to push the boundaries in what they send and to whom they send it.

"It is now so easy to send pictures instantly via e-mails and texts that we are seeing instances of boys or girls sending sexual images of themselves to others without considering the consequences.

"They often find out later that the image has been passed on to many others and as a result they can be the victims of bullying or harassment.

"In some rare instances we have seen these images end up in the collections of offenders."

Crime Prevention minister James Brokenshire said that the sending of such explicit messages was a "worrying trend".

He said: "We should encourage young people to use technology but it's really important that they are made aware of the dangers involved too."

Meanwhile, the UK Council for Child Internet Safety (UKCCIS) has launched guidelines on how to moderate online environments for children.

Children's minister Tim Loughton said: "We are working with business to make sure children and young people are safe online.

"The UK Council for Child Internet Safety are today publishing guidelines on keeping online environments safe for children. I warmly welcome this first step in industry self-regulation."